Measurements of the R–NO bond dissociation energy in some halogenated C-nitroso-compounds and in di-t-butyl nitroxide have been made using an electron impact method. The values obtained are: 31 kcal mol–1 for D(CF3–NO), 32 for D(CCl3–NO), 62 for D(C6F5–NO), and 29 for D(ButNO–But). These values are compared with bond dissociation energies in a range of other nitroso-compounds, and general relationships between structural parameters and bond dissociation energies are discussed. The anomalous value for D(C6F5–NO) is discussed.